The present invention relates to a novel AB2 monomer, which can be polymerized to form hyperbranched polyimides.
Aromatic polyimides (Pls) are well known, high-performance materials with widespread applications in the aerospace and electronics industries due to their excellent thermomechanical and dielectric properties. Recently, it was demonstrated that they are useful as optical materials based on their optical anisotropy when cast in directions parallel (in-plane) and perpendicular (out-of-plane) to the film surface. However, when fully imidized, most aromatic Pl""s have limited solubility in common organic solvents, thus restricting the choice in processing options. Numerous research efforts have focused on organo-soluble Pls from the modification of the structure without substantially decreasing rigidity of their backbone. Solubility is desired in order to allow processing polymers with preformed imide units and to avoid the problems associated with handling poly(amic acid) (PAA) precursors. In addition, homogeneous, post-polymer reactions of soluble aromatic polyimides would allow better control in the introduction of desirable functional groups.
A viable alternative to attaining solubility in aromatic Pls is to change the traditional, linear geometry of the macromolecules to three-dimensional, highly branched (dendritic) architecture. As a subset of dendritic polymers, hyperbranched polymers have several important advantages such as better solubility compared to their linear counterparts, and easier synthesis than their analogous dendrimers, which involve tedious multi-step synthesis. Large quantity of hyperbranched polymers can be easily produced from ABx (xxe2x89xa72) monomers. There are few reports on synthesis of hyperbranched Pls, and their utilization.
Accordingly, it is an object of the present invention to provide a self-polymerizable AB2 monomer.
Other objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
In accordance with the present invention there is provided a self-polymerizable AB2 monomer of the formula 
Synthesis of the AB2 monomer of this invention, N-{3,5-bis(4-hydroxybenzoyl)benzene}-4-fluoroisophthalimide, is shown by the following reaction sequence: 
In this sequence, 5-nitroisophthalic acid is first treated with thionyl chloride (reaction a) to provide 5-nitroisophthaloyl dichloride (1). Friedel-Crafts reaction of 1 with anisole in the presence of aluminum chloride (reaction b) gives 3,5-bis(4-methoxybenzoyl)nitrobenzene (2), which is then demethylated with pyridine hydrochloride (reaction c) to provide 3,5-bis(4-hydroxybenzoyl)nitrobenzene (3). Compound 3 is then reduced (reaction d) to 3,5-bis(4-hydroxybenzoyl)aniline (4). Upon reacting with 4-fluoroisophthalic anhydride, with catalytic amount of isoquinoline, 4 is converted to the monomer 5, N-{3,5-bis(4-hydroxybenzoyl)benzene}-4-fluoroisophthalimide (reaction e).
The resulting AB2 monomer can be polymerized in the presence of potassium carbonate under Dean-Stark conditions to afford high molecular, low viscosity hyperbranched ether-ketone-imide polymer having repeating units with hydroxyl endgroups: 
These endgroups can be readily converted to other useful and thermally reactive groups, such as, for example, 
The polymers with reactive endgroups are key components of high-temperature matrix resins such as cyanate ester resins, phthalonitrile- and benzoxazine-based thermosets, and the like.